ABSTRACT The long-term objectives of this project are to acquire fundamental knowledge about the role of aryl hydrocarbonreceptor(AHR)inenergymetabolismandtobetterunderstandthemechanisticunderpinningsof metabolic disease. The AHR is a ligand-activated transcription factor that regulates gene expression via site- specific DNA binding. Recent data have implicated the AHR in transcriptional modulation of the metabolic hormone fibroblast growth factor 21 (FGF21). FGF21 is secreted from the liver and promotes a thermogenic brownadiposetissue-likephenotypeinwhitefatdeposits.ExogenousFGF21administrationinvariousmodels of obesity consistently results in reduced weight gain and fat deposition. My previous data indicate that the activationofFgf21geneexpressionbyseveraldifferenttranscriptionfactorsisattenuatedwithpre-exposureto AHRagonist,butthemechanismforthisisunclear.Sincetheoriginalsubmission,Ihavegenerateddatathat demonstrateAHRlosspromotesweightloss,hepatocyteFGF21output,andtheformationofabrownadipose tissue-likephenotypeinperigonadalwhiteadiposetissue(gWAT).Utilizingahepatocyte-targetedAHR-FGF21 doubleknockout(DKO)mousemodel,IfurthershowthatthisphenotypeisdependentuponFGF21expression. Preliminary data indicate that AHR loss protects against a high-fat diet (HFD) challenge by reducing weight gainandadiposity.TheunderlyinghypothesisoftheproposedresearchisthatAHRlossreleasesconstitutive AHR-dependent suppression of Fgf21 transcription to protect against HFD-induced obesity. To test this hypothesis, two specific aims are proposed. The first specific aim will characterize how AHR deletion can protect against high-fat dietary challenge through increased hepatocyte FGF21 production, and employs a sophisticated in vivo methodology to reintroduce AHR expression into AHR-deficient mice and FGF21 expression into DKO mice. Specific aim two will interrogate the mechanism via which the AHR modulates Fgf21 transcription within a native chromatin setting. Chromatin immunoprecipitations and state-of-the-art CRISPR/Cas9 gene-editing techniques will be used in this aim to reconcile AHR agonist-driven changes in Fgf21 gene expression with temporal AHR binding events at three specific DREs within the Fgf21 promoter. Successful completion of the proposed studies will provide a comprehensive assessment of how the AHR modulateshepaticFgf21expression,helpcultivateabettermolecularunderstandingoftheroleoftheAHRin energy homeostasis, and may identify the AHR as a potential ?druggable? target in the development of therapeutic treatments against metabolic disease. Consistent with the applicant?s career development objectives, the proposed innovative experiments and mentored training plan are tailored to provide training in sophisticatedtechniquesandtoaidinthetransitiontoindependence.